A thin-film capacitor including a dielectric layer formed of a perovskite-type ferroelectric oxide thin film such as a paraelectric strontium titanate (SrTiO3) thin film or a ferroelectric strontium barium titanate ((Ba,Sr)TiO3) thin film (hereinafter also referred to as “BST film”) has been proposed (e.g., refer to Japanese Unexamined Patent Application Publication No. 8-340090). A variable capacitor has also been proposed in which its capacitance characteristic is controlled by controlling the dielectric constant of the dielectric layer by applying a particular bias signal (bias voltage) to the dielectric layer (e.g., refer to Japanese Unexamined Patent Application Publication No. 11-260667). Also proposed is a variable capacitor in which a plurality of variable capacitor elements are connected in series, an external connecting electrode is disposed on a supporting substrate, and the variable capacitor elements are covered with an interlayer insulating film and a protective film (e.g., refer to Japanese Unexamined Patent Application Publication No. 2004-207630).